warnings' FATAL has lexical scope, so unless the module provides a custom sub import that allows the person useing the module to turn them on, the user of the module can't do so. And they also don't fatalize warn statements.

$ perl -Mstrict -Mwarnings=FATAL,all -le 'warn "Hello";my $x=1+"";prin
+t $x'
Hello at -e line 1.
Argument "" isn't numeric in addition (+) at -e line 1.
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